Microwave oven control system

ABSTRACT

A control circuit for a microwave oven is disclosed which functions to automatically control the running time of the microwave generator to enable it to run continuously, during its cooking cycle, or intermittently, during its defrosting cycle. The control circuit includes a timer control switch operatively coupled to a timer motor. The timer control switch functions to control the current flow from the source of electrical power to the microwave generator. The circuit also includes a defrost control switch which functions to cyclically open and close a series current path to the microwave generator. A bypass circuit is also provided across the defrost control switch to shortcircuit the defrost switch and provide a bypass current path to the microwave generator. A &#39;&#39;&#39;&#39;cook-defrost&#39;&#39;&#39;&#39; switch is provided to connect the circuit to the bypass circuit for the cooking mode, or to disconnect the bypass circuit to enable the current path to be governed by the defrost control switch for the defrosting mode. In one embodiment, the defrost control switch is coupled to a second timer motor which, in turn, is adapted to be cut into and out of the circuit by the &#39;&#39;&#39;&#39;cook-defrost&#39;&#39;&#39;&#39; switch. In a second embodiment, the defrost control switch is coupled to the first timer motor and is continuously operated thereby.

United States Patent [191 Tapper i 111 3,824,365 [451 July 16, 1974MICROWAVE OVEN CONTROL SYSTEM [75] Inventor: William R. Tapper, NewBrighton,

Minn.

[73] Assignee: Litton Systems, Inc., Beverly Hills,

Calif.

[22] Filed: Dec. 7, 1972 [21] Appl. N0.: 313,188

[52] US. Cl. 219/1055, 200/38 B [51] Int. Cl. H05b 9/06 [58] Field ofSearch 2l9/l0.55; 200/38 B, 38 BA,

200/38 C, 38 CA, 38 FA [56] References Cited UNITED STATES PATENTS3,324,273 6/1967 Ogburn 219/1055 3,470,942 10/1969 Fukada et al.219/1055 X 3,569,656 3/1971 White 219/1055 3,694,608 9/1972 Loubert etal. 219/1055 Primary Examiner-Elliot Goldberg Assistant ExaminerHugh D.Jaeger Attorney, Agent, or FirmRobert M. Vargo [57] ABSTRACT A controlcircuit for a microwave oven is disclosed which functions toautomatically control the running time of the microwave generator toenable it to run continuously, during its cooking cycle, orintermittently, during its defrosting cycle. The control circuitincludes a timer control switch operatively coupled to a timer motor.The timer control switch functions to control the current flow from thesource of electrical power to the microwave generator. The circuit alsoincludes a defrost control switch which functions to cyclically open andclose a series current path to the microwave generator. A bypass circuitis also provided across the defrost control switch to short-circuit thedefrost switch and provide a bypass current path to the microwavegenerator. A cook-defrost" switch is provided to connect the circuit tothe bypass circuit for the cooking mode, or to disconnect the bypasscircuit to enable the current path to be governed by the defrost controlswitch for the defrosting mode. In one embodiment, the defrost controlswitch is coupled to a second timer motor which, in turn, is adapted tobe cut into and out of the circuit by the cook-defrost switch. In asecond embodiment, the defrost control switch is coupled to the firsttimer motor and is continuously operated thereby.

21 Claims, 2 Drawing Figures MICROWAVE GENERATING v SYSTEM PATENIEU Juu61974 MICROWAVE GENERATING SYSTEM MICROWAVE GENERATING SYSTEM 1MICROWAVE OVEN CONTROL SYSTEM BACKGROUND OF THE INVENTION 1. Field ofthe Invention The present invention relates generally to microwavecooking ovens and more particularly to systems for controlling theoperating cycle of the microwave generators.

2. Description of the Prior Art It has been found that in defrostingfrozen products within a microwave cooking oven, the heating cannot becontinuous but must be intermittent in order to enable the heat absorbedin each frozen product to be distributed throughout the body of theproduct. If standing times were not permitted to allow for this heatdistribution, the exterior surfaces of the product would be entirelycooked, while the center would still be frozen.

Heretofore, defrosting operations conducted in microwave ovens had to beperformed manually. In other words, the operator had to set the timer onthe oven to a very short time (approximately one minute), then time thestanding time with an independent timer, and repeat this process as manytimes as necessary to accomplish complete defrosting. This, of course,is very cumbersome, since it requires the constant attention of theoperator. As a result, defrosting of frozen products, especially largefrozen products, was highly impractical.

SUMMARY OF THE INVENTION The present invention obviates theabove-mentioned short-comings by providing a microwave oven having acontrol system which enables both the cooking and defrosting cycles tobe accomplishedautomatically.

In its broadest aspect, the present invention comprises a microwave ovencontrol circuit having a defrost control switch for opening and closinga current path between the power supply and the microwave generator, anda bypass circuit to short-circuit the defrost control switch and providea bypass current path to the microwave generator. A cook-defrost switchis provided to selectively connect the circuit to the bypass circuit forthe continuous cooking mode, or to disconnect the bypass circuit toenable the current path to be operated intermittently by the defrostcontrol switch for the defrosting mode.

The features of the present invention which are believed to be novel areset forth with particularity in the appended Claims. The presentinvention, both as to its organization and manner of operation, togetherwith the further advantages thereof, may best be understood by referenceto the following description, taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of thecontrol circuit for a microwave oven of the present invention; and

FIG. 2 is a schematic view of a second embodiment of the control circuitfor a microwave oven of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,FIG. 1 illustrates a control circuit generally indicated by arrow forcontrolling the on-time of a microwave generating system 11. Shownschematically, the microwave generating system 11 is conventional inconstruction and typically includes a magnetron for emitting microwavesinto an oven cavity.

The control circuit 10 includes a two-part power line 13 and 15, the twoparts being connected at their one ends to a source of electric power17. Three lines 19, 21, and 23 are connected in parallel across thelines 13 and 15. The first line 19 includes a manual cook" switch 25which is normally biased in an open position, a timer control switch 27,and a relay coil 33. The cook switch 25 is preferably positioned tophysically extend through the control panel of the oven. A bypass line29 is connected across the cook switch 25 and includes a normally openrelay switch 31.

A second normally open relay switch 35 is located on the power line 13between the parallel lines 19 and 21. Both of the relay switches 31 and35 are operatively coupled to the relay coil 33 to be closed therebywhen energized.

The timercontrol switch 27 is mechanically coupled to a timer motor 37which is located across the line 23.

This coupling is accomplished by means of a cam 38 mounted on the outputshaft of the timer motor 37. The angular position of the timer motor 37and its cam 38 are adapted to be manually set by an interconnected dialwhich is preferably adapted to extend through the control panel of theoven. The cam 38 is adapted to be circular in shape with a singleprojection or cut-out located on the periphery thereof. The projectionis adapted to trigger the timer control switch 27 at the end of the camtravel.

The line 21 includes a defrost timer motor 39 which is mechanicallycoupled to a defrost control switch 41 to open and close the currentpath through that portion of the power line 13 extending between theparallel lines 21 and 23. As in the prior instance, this mechanicalcoupling is accomplished by a cam 40 mounted on the output shaft of thedefrost timer motor 39. The cam 40 is irregularly shaped to have a lowerand upper cam surface, each representing half of the total cam travel.The cam 40 then functions to open and close the switch once for each camrevolution. For convenience, a conventional minute-timer motor rotatinga one RPM is provided to enable the defrost control switch 41 to operatein 30-second equal cycles.

A cook-defrost switch 43 is provided to operate in a first position,which closes the line 21 to energize the defrost timer motor 39, and asecond position to interconnect the portion of the line 21 connected tothe power line 13 with a lead 45 which, in turn, is connected to theline 23. For convenience, this current path shall be called the bypasscircuit which functions to short-circuit the defrost control switch 41and enable current to be bypassed to the timer motor 37 and themicrowave generating system 11. It is preferable to have thecook-defrost switch 43 also extend through the control panel of theoven.

In operation when it is desired to operate the microwave oven in itscooking "cycle, the timer dial on the control panel is first set to asetting corresponding to the duration of oven on-time desired. Thisaction sets the cam 38 of the timer motor 37 to a predetermined positionwhich in turn closes the timer control switch 27. The cook switch 25 isthen depressed to close the line 19 and activate the relay coil 33. Uponactuation the relay coil 33 closes the relay switches 31 and 35.

The first relay switch 31 functions to keep the line 19 closed after thecook switch 25 is released. The line 19 will remain closed until thetimer control switch 27 is again opened by the timer motor 37. Thesecond relay switch 35 functions to close the power line 13 to enablecurrent to pass therethrough. t

In the cooking cycle, the cook-defrost switch 43 is in its secondpositionto enable current to pass through the bypass circuit to energizethe timer motor 37 and the microwave generating system 11. Currentcontinues to be fed to the microwave generating system .11 until the cam38 on the timer motor 37 reaches its zerotime position to open the timercontrol switch 27. This action functions to open the line 19 andde-energize the relay coil 33, thereby releasing the first and secondrelay switches 31 and 35. As a result, the line 19 is maintained in anopen position and the power line 13 is opened. The opening of the line13 stops the current flow to the timer motor 37 and the microwavegenerating system 11, thereby shutting off the magnetron locatedtherein. As can be seen, the microwave generating system 11-is dependentonly upon the operation of the timer control switch 27 during the cookcycle, and the operation of the oven is continuous.

In the defrost mode, the timer dial is again set as before to close thetimer control switch 27. The manual cook switch 25 is then depressed toenergize the relay the cook-defrost switch 43 is opened to enable thecurrent path to be controlled'by the defrost control switch 41. Theoperation of the manual cook switch 25, the timer control switch 27, andthe relay switches 31 and 35 all function in the same manner asdescribed in the first embodiment. i

In the second embodiment, the earns 38 and 40 can be coupled to thetimer motor 37 through gear train in order to slow down their rotationalspeed with respect to the speed of the timer motor 37 In thisembodiment, the speed of the defrost cam 40 is sufficiently slowed downto enable the cam 40 to be profiled with a plurality of cam projectionsspaced about the periphery thereof. As in the first embodiment, thedefrost cam 40 is profiled to enable the defrost control switch 41 to besequentially opened and closed at 30 second intervals.

coil 33 and close the relay switches 31 and 35. The

cook-defrost switch 43 is then manually depressed to move to its firstposition as shown on FIG. 1. In this position, current'is fed tothe'line 19 to energize the de- In the closed position of the defrostcontrol switch 41, current passes through the line 13 to the timer motor37 and the microwave generating system 11. As stated previously, the camand the speed of the defrost timer motor 39 cooperate to cause the timermotor 37 and the microwave generating system to operate intermittently;i.e., 30 seconds on and 30 seconds off. After the timer motor 37 hasbeen on the duration predetermined by the dial setting, the cam 38reaches its zero-time position to open the timer control switch 27,which in turn releases the relay switches 31 and 35 through the relaycoil 33.

The second embodiment of the present invention is shown in FIG. 2. Inthis embodiment, the second timer motor 39 is eliminated and the defrostcontrol switch 41 is mechanically coupled to the first timer motor 37.Since the timer motor 37 is continuously running during the operation ofthe oven, the defrost control switch 41 is continuously opening andclosing. This is different than the operation of the'first embodiment inwhich the defrost timer motor 39 was inactivated during the cookingcycle and the defrost control switch 41 did not operate. In the secondembodiment, the bypass circuit 45 is provided to again extend across thedefrost'control switch 41 to short-circuit the defrost cycler switch 41.As a result, during the cooking cycle, the cookdefrost switch 43 isclosed to provide a current path to the microwave generating system 11independent of the defrost control switch 41. During the defrost cycle,

As shown in FIG. 2, the oven control system 10 further includes a thirdcam 47 connected to the output shaft of the timer motor 37. The thirdcam 47 is operatively coupled to the defrost-cook switch 43 toautomatically open and close the switch'43. In its preferable mode ofoperation, the defrost-cook switch 43 is manually opened to initiate thedefrost cycle. The angular position of the cam 47 is then set to apredetermined setting, deemed sufficient to allow the frozen product 4within the oven to be completely defrosted. As with the timer controlcam 38, the cam 47 has a single projection at its zero time position toclose the defrost-cook switch 43 and enable the oven to automaticallyswitch to the cooking mode.v

As can be seen, the present invention provides a microwave oven thatfunctions automatically in both the cooking and defrosting modes.

It should be noted that various modifications can be made to theapparatus while still remaining within the purview of the followingclaims.

What is claimed is:

1. A microwave oven defrosting and cooking cycle control systemcomprising:

a microwave oven;

a microwave generating system for said microwave oven;

a current path coupling said microwave generating system to a source ofelectrical energy;

timer control switch means for opening and closing said current path;

defrost control switch means for opening and closing said current path;and

bypass circuit means extending across said defrost switch means forshort-circuiting said defrost switch means to enable said current pathto be selectively controlled by said timer control switch means in onemode and by both control switch means in a second mode.

2. The invention of claim 1 further comprising means for cyclicallyopening and closing said defrost control switch. r

3. The invention of claim 1 further comprising a defrost-cook switchmeans for cutting said bypass circuit into and out of said current path.

4. The invention of claim 3 further comprising means for automaticallyopening and closing said defrost-cook switch means.

5. Theinvention of claim 1 wherein said timer control switch is coupledto a first timer to be governed thereby.

6. The invention of claim 5 wherein said first timer comprises amotor-cam assembly operatively coupled to said timer control switchmeans.

7. The invention of claim 5 wherein said defrost control switch means iscoupled to a second timer to be governed thereby.

8. The invention of claim 7 wherein said second timer comprises a secondmotor-cam assembly operatively coupled to said defrost control switchmeans.

9. The invention of claim 5 wherein said defrost control switch means iscoupled to said first timer to be governed thereby.

10. The invention of claim 9 wherein said first timer comprises a motorcoupled to a pair of cam members, each cam member being mechanicallycoupled to said respective switch control means.

11. The invention of claim 10 further comprising:

a defrost-cook switch means for cutting said bypass circuit into and outof said current path; and

a third cam member coupled to said first timer motor, said third cambeing operatively coupled to said defrost-cook switch means forautomatically opening and closing said defrost-cook switch means.

12. A control circuit for coupling a power supply to a microwavegenerator comprising:

a pair of power lines interconnecting the power supply to a microwavegenerator;

a first line connected in parallel to said pair of power lines, saidfirst line having a timer control switch and a relay coil locatedthereon;

a holding contact switch serially connected to one of said power lines,said contact switch being operatively coupled to said relay coil;

a second line connected in parallel to said pair of parallel linesbeyond said holding contact switch with respect to the power supply,said second line having a first timer motor coupled thereto, said firsttimer motor being operatively coupled to said timer control switch;

a defrost control switch serially connected to one of said power linesbeyond said second line with respect to the power supply; and

a bypass circuit for selectively shortcircuiting said defrost controlswitch.

13. The invention of claim 12 further including a defrost-cook switchfor opening and closing said bypass circuit.

14. The invention of claim 12 wherein said first timer motor ismechanically coupled to said defrost control switch.

15. The invention of claim 12 wherein said first line .further includesa switch connected across said first line, said switch being biased inthe open position, and a bypass circuit having a second holding contactswitch coupled thereto, said second holding contact switch beingoperatively coupled to said relay coil.'

16. A control circuit for coupling a power supply to a microwavegenerator comprising:

a pair of power lines'interconnecting the power supply to a microwavegenerator;

a first line connected in parallel to said pair of power lines, saidfirst line having a timer control switch and a relay coil locatedthereon;

a holding contact switch serially connected to one of said power lines,said contact switch being operatively coupled to said relay coil;

a second line connected in parallel to said pair of parallel linesbeyond said holding contact switch with respect to the power supply,said second line having a defrost timer motor coupled thereto;

a defrost control switch serially connected to one of said power linesbeyond said second line with respect to the power supply, said defrosttimer motor being operatively coupled to said defrost control switch;and

a third line connected inparallel to said pair of power lines beyondsaid defrost control switch with respect to the power supply, said thirdline having a timer motor coupled thereto, said timer motor beingoperatively coupled to said timer control switch.

17. The invention of claim 16 further including a defrost-cook switchfor opening and closing said bypass circuit.

18. The invention of claim 17 wherein said bypass circuit comprises alead interconnecting said second line to said third line.

19. The invention of claim 18 wherein said cookdefrost switch is adaptedto interconnect in one position, the second line with said lead.

20. The invention of claim 19 wherein said cookdefrost switch is adaptedto interconnect, in a second position, the power line with the defrosttimer motor.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO.5,53%,365 DATED July 16, 197A INVENTOR(S) William R. Tapper It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

21. A microwave oven comprising:

a source of microwave energy;

a control circuit including a cyclically operated switch for energizingthe source of microwave energy in a mode of intermittent energization ofthe source of microwave energy;

a bypass circuit path shunting the cyclically operated switch; and

a mode selector switch in the bypass circuit path for closing the bypasscircuit path to initiate and maintain continuous operation of the sourceof microwave energy in a mode of continuous operation.

Signed and sealed this 10th day of June 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officerand Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,82 r,565 DATED July 16, 197

iN\ ENTOR(S) William R. Tapper it is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

21. A microwave oven Comprising:

a source of microwave energy; 7

a controlv circuit including a cyclically operated switch for energizingthe source of microwave energy in a mode of intermittent energization ofthe source of microwave energy;

a bypass circuit path shunting the cyclically operated switch; and

a mode selector switch in the bypass circuit path for closing the bypasscircuit path to initiate and maintain continuous operation of the sourceof microwave energy in a mode of continuous operation.

Signed and sealed this 10th day of June 1975.

(SEAL) Attest:

C. MARSHALL DANN Commissioner of Patents and Trademarks RUTH C. MASONAttesting Officer

1. A microwave oven defrosting and cooking cycle control systemcomprising: a microwave oven; a microwave generating system for saidmicrowave oven; a current path coupling said microwave generating systemto a source of electrical energy; timer control switch means for openingand closing said current path; defrost control switch means for openingand closing said current path; and bypass circuit means extending acrosssaid defrost switch means for short-circuiting said defrost switch meansto enable said current path to be selectively controlled by said timercontrol switch means in one mode and by both control switch means in asecond mode.
 2. The invention of claim 1 further comprising means forcyclically opening and closing said defrost control switch.
 3. Theinvention of claim 1 further comprising a defrost-cook switch means forcutting said bypass circuit into and out of said current path.
 4. Theinvention of claim 3 further comprising means for automatically openingand closing said defrost-cook switch means.
 5. The invention of claim 1wherein said timer control switch is coupled to a first timer to begoverned thereby.
 6. The invention of claim 5 wherein said first timercomprises a motor-cam assembly operatively coupled to said timer controlswitch means.
 7. The invention of claim 5 wherein said defrost controlswitch means is coupled to a second timer to be governed thereby.
 8. Theinvention of claim 7 wherein said second timer comprises a secondmotor-cam assembly operatively coupled to said defrost control switchmeans.
 9. The invention of claim 5 wherein said defrost control switchmeans is coupled to said first timer to be governed thereby.
 10. Theinvention of claim 9 wherein said first timer comprises a motor coupledto a pair of cam members, each cam member being mechanically coupled tosaid respective switch control means.
 11. The invention of claim 10further comprising: a defrost-cook switch means for cutting said bypasscircuit into and out of said current path; and a third cam membercoupled to said first timer motor, said third cam being operativelycoupled to said defrost-cook switch means for automatically openiNg andclosing said defrost-cook switch means.
 12. A control circuit forcoupling a power supply to a microwave generator comprising: a pair ofpower lines interconnecting the power supply to a microwave generator; afirst line connected in parallel to said pair of power lines, said firstline having a timer control switch and a relay coil located thereon; aholding contact switch serially connected to one of said power lines,said contact switch being operatively coupled to said relay coil; asecond line connected in parallel to said pair of parallel lines beyondsaid holding contact switch with respect to the power supply, saidsecond line having a first timer motor coupled thereto, said first timermotor being operatively coupled to said timer control switch; a defrostcontrol switch serially connected to one of said power lines beyond saidsecond line with respect to the power supply; and a bypass circuit forselectively shortcircuiting said defrost control switch.
 13. Theinvention of claim 12 further including a defrost-cook switch foropening and closing said bypass circuit.
 14. The invention of claim 12wherein said first timer motor is mechanically coupled to said defrostcontrol switch.
 15. The invention of claim 12 wherein said first linefurther includes a switch connected across said first line, said switchbeing biased in the open position, and a bypass circuit having a secondholding contact switch coupled thereto, said second holding contactswitch being operatively coupled to said relay coil.
 16. A controlcircuit for coupling a power supply to a microwave generator comprising:a pair of power lines interconnecting the power supply to a microwavegenerator; a first line connected in parallel to said pair of powerlines, said first line having a timer control switch and a relay coillocated thereon; a holding contact switch serially connected to one ofsaid power lines, said contact switch being operatively coupled to saidrelay coil; a second line connected in parallel to said pair of parallellines beyond said holding contact switch with respect to the powersupply, said second line having a defrost timer motor coupled thereto; adefrost control switch serially connected to one of said power linesbeyond said second line with respect to the power supply, said defrosttimer motor being operatively coupled to said defrost control switch;and a third line connected in parallel to said pair of power linesbeyond said defrost control switch with respect to the power supply,said third line having a timer motor coupled thereto, said timer motorbeing operatively coupled to said timer control switch.
 17. Theinvention of claim 16 further including a defrost-cook switch foropening and closing said bypass circuit.
 18. The invention of claim 17wherein said bypass circuit comprises a lead interconnecting said secondline to said third line.
 19. The invention of claim 18 wherein saidcook-defrost switch is adapted to interconnect in one position, thesecond line with said lead.
 20. The invention of claim 19 wherein saidcook-defrost switch is adapted to interconnect, in a second position,the power line with the defrost timer motor.
 21. A microwave ovencomprising: a source of microwave energy, a control circuit including acyclically operated switch for energizing the source of microwave energyin a mode of intermittent energization of the source of microwaveenergy, a bypass circuit path shunting the cyclically operated switch,and a mode selector switch in the bypass circuit path for closing thebypass circuit path to initiate and maintain continuous operation of thesource of microwave energy in a mode of continuous operation.